I’m having trouble with my wheel pins cracking the wheel rims as I drive them in. The pins I print measure 16.06mm x 19.96mm x 38.74mm. The STLs are 16.05mm x 20.04mm x 38.75mm (+0.01mm, -0.08mm, -0.01mm).
The wheel pin slots are hard to measure, but the skinny side of the pin measures 16.00mm in my slicer.
I can try lower flow rates, but I’m concerned about structural integrity, especially with such low infill and perimeters on these parts.
I also don’t understand why the wheel pins, which are basically 100% solid PETG, have at most 0.08mm deviation on 20.04mm (0.3%), while the wheel rims, which are mostly open air, have a 0.15mm deviation on 16mm (~1%).
I’ll try a lower flow rate tonight and see what happens.
Most filaments print around that 95% range. I cant remember ever having one that printed above .98 at most. I really don’t think you will have any issues with structural integrity at .95. I have printed a few chairs with Numakers filament at that with zero issues.
I’ve printed 2 sets of wheels. The first was with Bambu Lab PETG and the pins were snug, but went in easy enough. The second set was with Numakers PETG, and I had to keep tapping the pins fairly hard with my rubber mallet to get them in. The rims didn’t crack, but I was worried they might. I didn’t sand or use Dry Lube but was about to when the pins went the rest of the way in when I used another Pin to serve like a nail punch so all the force hit the pin and none hit the rim.
I have noticed that wording on one of the sides (Rev…) of these pins is not flush with the surface, but sticks out by about 1/2mm. It’s more pronounced with 0.6mm nozzle. I sanded it down, and it seemed to eliminate cracking issue for me.
Few other tips:
Put a flat piece of wood under the bottom of the wheel when driving the pins in.
Make sure that they are driven in straight
Do not to drive each pin all the way in right away. Instead set them partially, and go in the round driving them in gradually.
Ditto, I also build the wheels on my bed or I use a dense foam under the wheel. This absorbs the shock and distributes the forces more evenly. I’ve had zero issues so far with two TMTs.
No, I don’t think people sand or use dry lube on every build. These are just two things I though of that might help answer the question about what can be done in this situation. I think most builders aren’t having the rims crack when they put the pins in without doing either of these.
That is going to be a challenge for sure. I don’t know what I’m doing, but I haven’t run into that issue. The connection piece for the handle - Yes - I have been VERY careful putting that together. That is the only part that gives me the cold sweats…
After much troubleshooting, I believe I figured out a bulk of the issue: a worn brass nozzle.
I print a lot of white ASA. Most white filaments get their color from titanium dioxide. Titanium dioxide is abrasive and wears brass nozzles. I knew that at some point I would need to change to something that resists abrasion, but I was waiting for more a more catastrophic failure as a signal. It turns out this was the signal.
I swapped in a tungsten carbide nozzle, which conducts heat similarly to brass, but is durable enough to outlast the heat death of the universe. Extrusion multiplier went from 1.015 to 0.985, which makes sense in the context of a worn nozzle. With a larger opening, more material needed to be extruded to produce consistent results in calibration tests.
Dimensional accuracy on the pins is better. The pins are now about 0.1mm undersized in the X and Y dimension. The wheel rim pin hole dimensions are still somewhat problematic. They’re still slightly undersized (15.95mm vs 16mm spec). Now that the pins are slightly undersized, this lines up better. But with a 16.06mm pin width and 16mm hole width, it’s still an extremely tight fit.
I’m now having some unrelated issues with the toolhead knocking over supports and crashing into the prints, but that’s unrelated to dimensional accuracy and nozzle wear. I’m cautiously optimistic that accuracy is close enough to finish the build.
That is going to be a challenge for sure. I don’t know what I’m doing, but I haven’t run into that issue. The connection piece for the handle - Yes - I have been VERY careful putting that together. That is the only part that gives me the cold sweats…